From ddc003380c8edaea116dbe92a1814a8d98681426 Mon Sep 17 00:00:00 2001
From: yuyi <yuyi98@163.com>
Date: Tue, 4 May 2021 00:48:54 +0800
Subject: [PATCH] checker: check generics fn that return generic struct (#9979)

---
 vlib/v/checker/checker.v                       |  9 +++++++++
 .../generics_fn_return_generic_struct_err.out  |  7 +++++++
 .../generics_fn_return_generic_struct_err.vv   | 18 ++++++++++++++++++
 3 files changed, 34 insertions(+)
 create mode 100644 vlib/v/checker/tests/generics_fn_return_generic_struct_err.out
 create mode 100644 vlib/v/checker/tests/generics_fn_return_generic_struct_err.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 02d52d7078..e0d0ba0555 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -6808,6 +6808,15 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			c.error('only functions that do NOT return values can have `[if $ct_name]` tags',
 				node.pos)
 		}
+		if node.generic_names.len > 0 {
+			gs := c.table.get_type_symbol(node.return_type)
+			if gs.info is ast.Struct {
+				if gs.info.is_generic && !node.return_type.has_flag(.generic) {
+					c.error('return generic struct in fn declaration must specify the generic type names, e.g. Foo<T>',
+						node.return_type_pos)
+				}
+			}
+		}
 	}
 	if node.is_method {
 		mut sym := c.table.get_type_symbol(node.receiver.typ)
diff --git a/vlib/v/checker/tests/generics_fn_return_generic_struct_err.out b/vlib/v/checker/tests/generics_fn_return_generic_struct_err.out
new file mode 100644
index 0000000000..12a579c300
--- /dev/null
+++ b/vlib/v/checker/tests/generics_fn_return_generic_struct_err.out
@@ -0,0 +1,7 @@
+vlib/v/checker/tests/generics_fn_return_generic_struct_err.vv:13:32: error: return generic struct in fn declaration must specify the generic type names, e.g. Foo<T>
+   11 | }
+   12 |
+   13 | pub fn new_channel_struct<T>() GenericChannelStruct {
+      |                                ~~~~~~~~~~~~~~~~~~~~
+   14 |     d := GenericChannelStruct{
+   15 |         ch: chan T{}
diff --git a/vlib/v/checker/tests/generics_fn_return_generic_struct_err.vv b/vlib/v/checker/tests/generics_fn_return_generic_struct_err.vv
new file mode 100644
index 0000000000..0f9a5d5f91
--- /dev/null
+++ b/vlib/v/checker/tests/generics_fn_return_generic_struct_err.vv
@@ -0,0 +1,18 @@
+struct GenericChannelStruct<T> {
+	ch chan T
+}
+
+struct Simple {
+	msg string
+}
+
+fn main() {
+	new_channel_struct<Simple>()
+}
+
+pub fn new_channel_struct<T>() GenericChannelStruct {
+	d := GenericChannelStruct{
+		ch: chan T{}
+	}
+	return d
+}